C. Declaring Variables

Estimated time: 7 minutes | Previous: B. Making a Game Window | Next: D. Making a 3D Cube with Entity

🎯 Learning Goals

By the end of this lesson, you'll be able to:

○ Understand what a variable is
○ = can store a value using the symbol
○ Can create variables of various types

Core Concepts

What is a variable?

Variableis a box that stores a value.

📝 Analogy: a box with a name tag

A variable is A box with a name tag on itis the same as!

cube_sizeinto a box with the name tag, put the number 2in it
Later, cube_size when you open the box, 2comes out
You can change the contents of the box anytime

Use them to store things like score, health, and color in a game!

Variable usage flowchart

flowchart LR
    A["Variable name"] --> B["="]
    B --> C["Value"]
    C --> D["Stored!"]

    E["cube_size"] --> F["="]
    F --> G["2"]
    G --> H["Store 2 in cube_size"]

    style A fill:#e3f2fd,stroke:#1976d2
    style E fill:#e3f2fd,stroke:#1976d2
    style C fill:#e8f5e9,stroke:#388e3c
    style G fill:#e8f5e9,stroke:#388e3c

Creating a variable

my_name = "Student"      # String variable
cube_size = 2            # Number variable
cube_color = color.red   # Color variable

Description:

= stores a value using the symbol
A variable name is like the label on a box
Later you can retrieve the value by its variable name

Types of variables

Types	Example	Description	Use
String	`"Student"`	Text wrapped in quotation marks	Names, messages
Integer	`2`	A number without a decimal point	Counts, sizes
Mistake	`3.14`	A number with a decimal point	Positions, speeds
Color	`color.red`	Ursina colors	Object colors

⚠️ Variable naming rules

Be careful when naming variables!

✅ Letters, numbers, and underscores (_) are allowed
✅ cube_size, myName, player1
❌ Cannot start with a number: 1cube
❌ Spaces are not allowed: cube size
❌ Special characters are not allowed: cube-size, cube@size

Example Code

from ursina import *

app = Ursina()

# Declare variables
my_name = "Student"
cube_size = 2
cube_color = color.red

# Use the variable
print(f"Name: {my_name}")
print(f"Size: {cube_size}")
print(f"Color: {cube_color}")

app.run()

Result

The variable values are printed to the console!

Name: Student
Size: 2
Color: (255, 0, 0, 255)

🎯 Quiz

Quiz: The role of a variable

cube_size = 2what is the role of the variable cube_sizein?

Show Answer

Answer: B) Stores the number 2

cube_size = 2is cube_sizeinto a variable with this name, the number 2is stored. Later, cube_sizeIf you use it 2you can retrieve this value!

🔧 Debug Clinic

Problem: NameError: name 'cube_colour' is not defined

Cause: Typo in the variable name (used British spelling)

Fix: Use the exact variable name

# ❌ Wrong code
cube_color = color.red
Entity(color=cube_colour)  # Typo! colour vs color

# ✅ Correct code
cube_color = color.red
Entity(color=cube_color)  # Correct name!

Problem: SyntaxError: invalid syntax

Cause: Used a space or special character in the variable name

Fix: Connect words with an underscore (_)

# ❌ Wrong code
cube size = 2      # Space used!
cube-size = 2      # Hyphen used!

# ✅ Correct code
cube_size = 2      # Underscore used!
cubeSize = 2       # camelCase is OK too

Try Coding It Yourself

Try writing code that declares and uses variables!

Declaring variables

Store the player's name and score in variables.

Example Answer

from ursina import *

app = Ursina()

player_name = "Hero"
player_score = 100

print(f"Player: {player_name}")
print(f"Score: {player_score}")

app.run()

Result: "Player: Hero" and "Score: 100" are printed to the console!

🧩 Key Takeaways

What you learned in this lesson:

Variable: A labeled box that stores a value
= Symbol: Stores the value on the right into the variable on the left
String: Text wrapped in quotation marks ("Hello")
Number: An integer (2) or a float (3.14)
Naming rules: Use only letters, numbers, and underscores (cannot start with a number)

Review Checklist

[ ] Can you explain what a variable is?
[ ] = Do you know the role of the symbol?
[ ] Can you tell the difference between a valid and an invalid variable name?

Next step: D. Making a 3D Cube with Entity →